The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions. Depending upon the medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Physicians use medical devices alone or in combination with drug therapies to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life.
Implantable medical devices are commonly used today to treat patients suffering from various ailments. Implantable medical devices can be used to treat any number of conditions such as pain, incontinence, movement disorders such as epilepsy and Parkinson's disease, and sleep apnea. Additional therapies appear promising to treat a variety of physiological, psychological, and emotional conditions. As the number of implantable medical device therapies has expanded, greater demands have been placed on the implantable medical device.
One type of implantable medical device is an Implantable Neuro Stimulator (INS). The INS delivers mild electrical impulses to neural tissue using an electrical lead. The neurostimulation targets desired neural tissue to treat the ailment of concern. For example, in the case of pain, electrical impulses (which are felt as tingling) may be directed to cover the specific sites where the patient is feeling pain. Neurostimulation can give patients effective pain relief and can reduce or eliminate the need for repeat surgeries and the need for pain medications.
Implantable medical devices such as neurostimulation systems may be partially implantable where a battery source is worn outside the patient's body. This system requires a coil and/or an antenna to be placed on the patient's skin over the site of the receiver to provide energy and/or control to the implanted device. Typically, the medical device is totally implantable where the battery is part of the implanted device. The physician and patient may control the implanted system using an external programmer. Such totally implantable systems include, for example, the Itrel® 3 brand neurostimulator sold by Medtronic, Inc. of Minneapolis, Minn.
In the case of an INS, for example, the system generally includes an implantable neurostimulator (INS) (also known as an implantable pulse generator (IPG)), external programmer(s), and electrical lead(s). The INS is typically implanted near the abdomen of the patient. The lead is a small medical wire with special insulation. It is implanted next to the spinal cord through a needle and contains a set of electrodes (small electrical contacts) through which electrical stimulation is delivered to the spinal cord. The lead is coupled to the INS via an implanted extension cable. The INS can be powered by an internal source such as a battery or by an external source such as a radio frequency transmitter. The INS contains electronics to send precise, electrical pulses to the spinal cord, brain, or neural tissue to provide the desired treatment therapy. The external programmer is a hand-held device that allows the physician or patient to optimize the stimulation therapy delivered by the INS. The external programmer communicates with the INS using radio waves.
One of the key troubleshooting tools for the clinicians for the stimulation devices is the lead impedance measurement. This measure is basically the electrical resistance of the leads plus that of the tissue contacts and provides important information regarding both the lead placement and the integrity of the lead itself.
A lead contains a plurality of electrodes, e.g. four electrodes. Some of the electrodes may be configured as being inactive. In previous programmer implementations, lead measurements were provided only for the currently programmed electrode configurations. Though this in itself provides some utility, various lead problems may be undetected. For example, an active electrode that is shorting to one or more inactive electrodes will not be detected by a single measurement such as previously provided.
Some clinicians circumvent this limitation by manually configuring each electrode pair and performing the single measure many times. For example, with a lead containing four electrodes, there are six electrode pairs (4!/(2!2!)). The number substantially increases as the number of electrodes increases. With a lead containing eight electrodes, there are twenty-eight electrode pairs (8!/(6!2!)). Each pair of electrodes requires that the clinician execute a number of operations through an input device. While efficacious, this manual process proves to be time consuming and tedious. Furthermore, all such measurements are performed at the current therapy settings, which may not be optimal for measurement accuracy and for the patient's comfort.